This is a randomized, double-blind, parallel-group, placebo-controlled, multi-center trial to evaluate the safety and efficacy of Leustatin tm (Cladribine) in subjects with chronic progressive multiple sclerosis. There will be three patient groups in the trial: (1) a placebo group: (2) a high dose treatment group, and (3) a low dose treatment group. The placebo group is necessary to establish the magnitude of changes in clinical endpoints that may occur in the absence of active treatment. Patients are being followed in a long-term, open-label extension. The drug did not receive approval from the FDA due to loack of efficacy. Patients will be followed for at least 2 more years.